In a first aspect, this invention pertains to a process of stabilizing an olefin metathesis product mixture, preferably, against double bond isomerization and thermal and chemical decomposition. In a second aspect, this invention pertains to a stabilized olefin metathesis product composition. In a third aspect, this invention pertains to methods for removing metals from an olefin metathesis product mixture.
Olefin metathesis processes commonly involve the conversion of two reactant olefins in the presence of a metathesis catalyst into one or more product olefins that are different from the reactant olefins. If the two reactant olefins are chemically different compounds, then the process is referred to as “hetero-metathesis.” If the two reactant olefins are chemically identical compounds, then the process is referred to as “homo-metathesis.” In a different, but yet related manner, olefin metathesis processes also include ring-opening metathesis polymerization reactions wherein an unsaturated cyclic compound is ring-opened and polymerized to form an unsaturated polymer. In yet another type of olefin metathesis process, a reactant alkene and reactant alkyne can be cross-metathesized to form a conjugated 1,3-diene. The prior art discloses homogeneous and heterogeneous metathesis catalysts that comprise at least one catalytically active metal, such as ruthenium, molybdenum, tungsten, or rhenium, and one or more ligands complexed to the metal(s).
Metathesis processes find utility in converting olefin feedstocks of low commercial value into unsaturated products of higher commercial value. By way of example, a long chain internal olefin, such as methyl oleate, obtainable from seed oils, can be metathesized with a lower olefin, such as a C2-8 olefin, preferably ethylene, in the presence of a metathesis catalyst to yield two product olefins of intermediate chain length, for example, 1-decene and methyl 9-decenoate. Intermediate length α-olefins, such as 1-decene, are useful in the preparation of poly(olefin) polymers. Alpha, omega (α,ω) ester-functionalized olefins, such as methyl 9-decenoate, can be converted into polyester polyepoxides, polyester polyalcohols or polyester polyamines, all of which find utility in the preparation of thermoset polymers, such as epoxy resins and polyurethanes.
Olefin metathesis product mixtures typically comprise one or more product olefins, a metal-ligand metathesis complex catalyst, optionally, metathesis catalyst degradation products, optionally, metathesis reaction by-products, and optionally, unconverted reactant olefins. As noted hereinabove, the metathesis catalyst comprises at least one catalytically active metal complexed to a catalytically active combination of one or more organic and/or inorganic ligands. Metathesis catalyst degradation products include ligand degradation products obtained when the ligand is oxidized by residual oxygen or otherwise reacted in a disadvantageous manner during the metathesis process. Metathesis degradation products may also include metal-ligand degradation product complexes. Finally, metathesis catalyst degradation products may also include catalytically inactive complexes produced when the catalytic metal binds to any available ligand to form a catalytically inactive complex. Olefin metathesis product mixtures may also contain extraneous metals added as catalyst promoters to the metathesis process or leached into the metathesis reaction from a catalyst support, a heterogeneous catalyst, or reactors and conduit pipes.
Homogeneous catalysts, while particularly active and selective, present a problem in that for economical purposes, the catalyst (including catalytic metal) should be recovered from the olefin metathesis product mixture. More importantly, it has been recognized that metathesis catalysts and catalyst degradation products destabilize olefin metathesis product mixtures against isomerization (double bond migration), which produces undesirable isomeric by-products different from the target products or the reactant olefins, as the case may be. Such undesirables reduce product selectivity and waste raw materials. The destabilization is generally more pronounced at elevated temperatures. Since product separation by distillation typically requires a higher temperature than that of metathesis, destabilization is more likely during the separation process. As a further disadvantage, metathesis catalysts and catalyst degradation products can destabilize olefin metathesis product mixtures against thermal and chemical decomposition. Over time, during storage or at elevated temperatures, undesirable thermal or chemical reactions may occur, further resulting in unrecoverable raw material losses and low product olefin yields. Such adverse effects are generally attributed to the presence of the catalytic metal(s) in the metathesis catalyst and catalyst degradation products. Similar adverse effects can also be induced by promoter metals that are deliberately added to the metathesis reaction to enhance catalyst performance or by extraneous metals that leach into the metathesis reaction mixture from catalyst supports, heterogeneous catalysts, metallic reactors, pipes, and conduits. Accordingly, efforts have been made to stabilize olefin metathesis product mixtures against double bond isomerization and decomposition resulting from metal contaminants.
H. D. Maynard and R. H. Grubbs disclose in Tetrahedron Letters, 40 (1999), 4137-4140, purification of ring-closing metathesis products of metathesis reactions utilizing a ruthenium catalyst. The purification involves treating the metathesis product mixture with a water-soluble phosphine, specifically, tris(hydroxymethyl)phosphine, followed by extraction with water so as to remove ruthenium into an aqueous phase. Disadvantageously, this method reduces the concentration of ruthenium by only one order of magnitude when an excess of 10 equivalents of water soluble phosphine is employed.
Leo A Paquette et al. discloses in Organic Letters, 2 (9) (2000), 1259-1261 the addition of lead tetraacetate to ring-closing metathesis product mixtures followed by filtration over silica gel to remove the colored ruthenium catalysts and impurities. The method teaches reduction of ruthenium residues by a factor of about 56. Disadvantageously, this method requires the use of lead tetraacetate under anaerobic conditions and thereafter a separate filtration step.
Yu Mi Ahn et al. discloses in Organic Letters, 3 (9) (2001), 1411-1413, a method of similar efficiency that involves treating the crude olefin metathesis product mixtures with triphenylphosphine oxide or dimethyl sulfoxide, followed by column chromatography on silica gel. Disadvantageously, this method employs a large quantity of triphenylphosphine oxide or dimethyl sulfoxide, both of which increase costs and add recovery steps to any commercial plan.
An earlier reference, U.S. Pat. No. 6,156,692 (filed 1997), drawn to a ring-opening polymerization of a cyclic olefin, discloses work-up of a crude polyolefin product over Darco™ brand charcoal. The reference teaches decolorizing the polymer, but does not address the problem of stabilizing an olefin metathesis product mixture against double bond isomerization and decomposition. Moreover, the final concentration of ruthenium in the polymer product (86 parts per million to 0.047 weight percent) is not sufficiently low to provide stabilization against double bond migration and decomposition.
In view of the prior art, it would be desirable to discover an improved method of stabilizing an olefin metathesis product mixture. It would also be desirable to discover an improved method of removing metals from olefin metathesis product mixtures. It would be more desirable if the improved method did not employ expensive reagents that require recovery. It would be even more desirable if the improved method did not employ large quantities of solvents or fluids that also increase costs and require recovery and recycle. It would be most desirable if the improved method could reduce the concentration of metal(s) in metathesis product mixtures more efficiently than prior art methods. At a high efficiency of metal removal, olefin metathesis product mixtures are more likely to be stabilized against double bond isomerization and chemical and thermal decomposition.